A normal functioning nervous system depends upon the production and assembly of appropriate types of neurons during development. The molecular mechanisms underlying these events, however, are poorly understood. Our ultimate goal is to understand the molecular basis of the generation of this precise cellular pattern. One approach is to capitalize on the advanced genetics and molecular biology of Drosophila to identify genes and gene products which control certain processes of neuronal development. To this end, we have identified and molecularly analyzed a gene, the singleminded (sim) gene, which controls the emergence and development of a specific subset of neuronal precursor cells which give rise to a set of unique progeny. We propose here to use molecular genetic and transformation techniques to study 1) the expression of the sim gene, 2) the fate of the sim-expressing cells in sim mutants, and 3) the function of the sim gene during neurogenesis. In addition, we will search for and analyze other genes related to sim. These experiments will provide us with a better understanding of how genes control the specification of particular sets of precursor cells within the developing nervous system. We expect that this information, in turn, will lead to an understanding of developmental strategies used in other nervous systems, including the human brain.